The present invention relates to the field of mass contact between at least two media and which may be used for a number of purposes such as the transfer of material, physical or chemical energy from one media to the next, such as, for example, the scrubbing of particulate from air by contact with water; humidifying a gas such as air by contact with water; distillation of volatile components of a liquid by contact with gas; heating or cooling a gas by contact with a warmer or cooler liquid and chemically reacting components contained in the two media.
There exists a number of other applications in which mass contact between media may be employed and it is contemplated that the present invention applies to all of such applications where mass contact between two or more media is desired.
Although the present invention will be described herein primarily making reference to mass contact between a liquid and a gas, such as water and air, for scrubbing, humidifying and/or cooling the air, it should be understood that the invention is not limited thereto.
The conventional approach to mass contact is to provide a vortical flow of gas in a chamber, suspend particles of liquid in the flow of gas and thereafter separate the liquid from the gas. Particulate carried by the gas can be taken up by the liquid to purify, i.e. "scrub", the gas. In addition, gaseous components soluble in the liquid can likewise be removed from the gas medium and the gas can be cooled by the liquid medium and/or humidified if the liquid is water. The present invention relates to such vortical flow type mass contact devices and more particularly, to mass contact devices employing entrainer/de-entrainer apparatus.
In U.S. Pat. No. 3,566,582, issued Mar. 2, 1971, reissued as RE 28,616 on Nov. 18, 1975 and assigned to the assignee of the present invention, there is described a mass contact device in which vortical gas flow is established by forcing a gas, such as air, through a louvered chamber, typically referred to as an annular vane cage, the vanes or louvers being oriented so that air or other gas entering the chamber in the open region or slots between the louvers has a directional flow imparted thereto, which directional flow has both radially inward and tangential directional vector components. The gas is thus caused to circulate about the interior of the chamber and ultimately exits through an axial opening at one end of the chamber, a vortical gas flow pattern thereby being established.
Liquid, such as water is drawn into the vortical gas flow which picks up the liquid and acts upon the liquid, creating a cloud-like suspension of liquid droplets throughout the vortical flow pattern. The droplets circulate with the gas and are concentrated in an annular zone inward from the louvered chamber.
The droplets are acted upon by the centripetal force of the radially inwardly directed component of gas flow, drawing the droplets inwardly of the vortex and ultimately out through the axial outlet opening of the vane cage and a centrifugal force created by the tangential component of the gas flow as well as the mass of the droplets which tend to cause the droplets to migrate outwardly of the vortex and toward the louvered wall. These effects cause a constant inward and outward migration of droplets within the suspended cloud, the migration being a function of droplet size.
The major influence on large droplets is the centrifugal force which causes large droplets to move outwardly and either strike inwardly moving droplets or the vane cage breaking up the droplets into droplets of smaller size. Droplets of smaller size and mass are principally influenced by the centripetal force vector of the vortical air flow. The droplets making up the cloud within the vane cage constantly change in the manner described wherein the proportion of inward and outward migration is a function of operational parameters which include the feed rate of the gas or air through the system, its pressure drop, the angle of the vanes and the dimension of the louvered chamber.
The scrubber vane cages are designed to provide optimum efficiency at a given air flow rating. The desired pressure drop of an entrainer vane cage and a de-entrainer vane cage for a given air flow rating is determined by the annular area of the vane cage which is a function of height and diameter.
Heretofore the accepted design approach was to make the vane cage substantially square in profile, i.e. the height of the vane cage is substantially equal to the diameter. Although the design approach provides optimum efficiency at the desired air flow rate, the efficiency drops considerably as the air flow rate deviates from the desired flow rate in both a positive (greater flow rate) or negative (smaller flow rate) direction, rendering conventional mass contact systems incapable of providing efficient operation over a broad air flow range.
The air vortex in the entrainment vane cage spirals upwardly through a central guide and exits through slots between the spaced apart vanes of a de-entrainment vane cage which imparts an expanding spiral impetus to the air as it leaves the de-entrainment vane cage and enters into an expansion chamber for ultimate egress from the de-entrainment tank.
The cloud moving from the entrainer to the de-entrainer includes water droplets together with air, the water droplets in the scrubber application carrying the particulate which is desired to be removed from the air.
Both large and small water droplets are transferred from the entrainer to the de-entrainer and reduce the efficiency of the de-entrainer and hence the scrubber by reducing the air passing through the de-entrainer vane cages.
The air leaving the de-entrainer vane cage swirls upwardly and egresses from the top of the de-entrainer tank whereas the water strikes the interior wall of the de-entrainment tank and eventually falls to the bottom of the de-entrainer tank where it is collected for filtration and is returned to the entrainer. The air which has been rid of the undesirable particulate is then safely returned to the atmosphere or to a utilization device for reuse. However, a significant amount of water passes through the outlet of the scrubber with the air which is disadvantageous.
The large amount of liquid introduced into the de-entrainer thus significantly reduces scrubber efficiency.